Signal transmission line



June 17, 1941.

H. K. KRIST SIGNAL TRANSMISSION LINE Filed April 3, 1940 nun N :i v

A T TORNEV Paten'ted June 17, 1941 UNITED ES, PATENT -OFFICE SIGNALTRANSMISSION LINE Henry K. Krist, Madison, N. J., assignor to BellTelephone Laboratories, Incorporated, New York, N. Y., a corporation ofNew York Application April 3, 1940, Serial No. 327,581

7 Claims.

This invention relates to signal transmission lines and particularly tosignal transmission lines having control circuits for automaticallycompensating for any change in loss on the transmission lines.

One object of the invention is to provide a signal transmission linehaving carrier and pilot,

channels thereon that shall control the iiat gain on the line accordingto the strength of one pilot current on the transmission line andcontrol the line attenuation characteristic according to the strength ofanother pilot current on the transmission line.

Another object of the invention is to provide a signal transmission linehaving carrier and pilot channels, a fiat gain ampliiier, a bulgenetwork and a slope network thereon that shall govern the amplifier, thebulge network and the slope network separately according to thestrengths of three pilot currents on the transmission line.

Another object of the invention is to provide a signal transmission linehaving carrier and pilot channels thereon that shall control the fiatgain on the line according to the strength of one pilot current, thatshall control the slope of the line attenuation characteristic accordingto the strength of another pilotl current on the line and that shallcontrol the bulge of the line attenuation characteristic according tothe strength of a third pilot current on the line.

A further object of the invention is to provide a signal transmissionline having carrier and pilot channels thereon that shall govern threelow frequency control circuits respectively according to the strengthsof three pilot currents on the line and that shall control the flat gainon the line, the slope of the line attenuation characteristic and thebulge of the line attenuation characteristic by said low frequencycircuits.

Long transmission systems such, for example, as carrier cable systemsare generally provided with flat gain and twist pilot wire regulatorswhich are located at intervals along the cable. These pilot wireregulators may be of the type disclosed in the F. A. Brooks Patent2,075,975, April 6, 1937. However, it is found that certain over-alllosses occur on the pairs of conductors making up a cable for whichcompensation is not effected.

According to the present invention, terminal or deviation regulators,which are controlled by pilot currents, are provided to compensate forover-al1 losses that are not corrected for by the ilat gain and twistregulators. The deviation regulators not only adjust the flat gain butalso the slope and bulge of the line attenuation characteristic. Y

In the carrier cable system employed to describe the invention, a gaincontrol amplier, a slope network and a bulge network are placed on eachpair of conductors in the cable at the terminal station. Each pair ofconductors in the cable is not only provided with carrier channels butalso with three pilot channels. The pilot currents on a pair ofconductors respectively control the amplier, the slope network and thebulge network on the associated pair of conductors.

A filter which selects the three pilot currents is connected to thetransmission line at a point beyond the flat gain ampliiier and theslope'and bulge networks. The transmission line may be a pair ofconductors in a carrier cable system. 'Ihe three pilot currents selectedby the filter are amplied and supplied to three auxiliary filters whichrespectively select the three pilot currents. The auxiliary iilter whichselects the pilot current controlling the flat gain ampliiier isconnected to a voltage doubler rectifier. The output from the voltagedoubler rectifier is opposed by a constant potential for impressing anegative bias on the control grid of a control amplifier. The outputfrom the voltage doubler rectier is opposed by a constant potential inorder to effect a more proportional change for any variation in thestrength in the pilot current.

The plate of the control vamplifier is supplied not only with directpotential but also with a low frequency alternating current preferably acycle power current. The output from the control amplier governs athermistor connected across the negative feedback circuit of the flatgain amplifier. An increase in the strength of the pilot current on thetransmission line which governs the at gain amplifier increasesr thenegative bias on the control amplifier. An increase in the strength ofthe negative bias on the control amplifier lowers the heating currentsupplied to the thermistor in the negative feedback circuit of the fiatgain ampliiier to increase the feedback and accordingly lower the gainof the amplier. An opposite effect takes place in case the strength ofthe pilot current on the transmission line is lowered.

The bulge network on the transmission line is controlled in asimilarrmanner to that of the flat gain amplier by another pilot currenton the transmission line. The auxiliary filter which selects the pilotcurrent governing the bulge network is connected to a voltage doublerrectiiier which controls the negative bias on a control ampliiier. Thecontrol amplifier governs the heating of a thermistor having a negativecoefficient of resistance which is included in the bulge network. Anincrease in the strength of the pilot current on the transmission linewhich controls the bulge network increases the negative bias onthecontrol grid of the control amplifier. A reduction in the output fromthe control amplifier lowers the heating of the thermistor in the bulgenetwork to increase the resistance thereon. An increase in theresistance of the thermistoiin the slope network increasesy the losseected by the bulge network. An opposite effect is produced in theoperation orf-the bulge network in case the strength of the pilotcurrent of the transmission line is lowered.

The auxiliary filter which selects the pilot current for controlling theslope network is connected to a voltage doubler rectifier which.impresses a negative bias on the grid of a control amplifier. Thecontrol amplifier governs a thermistor having anegative coefcient ofresistance in the slope network to control the operation of the network.The control ampliers employed for governing the slope and the bulgenetworks are each supplied with low frequency alternating current thesame as the control ampliiier em- .ployed to govern the flat gainamplilier so that the thermistors governing the slope and bulge networksare each controlled by circuits having low. frequency currents impressedthereon. 'Ilie thermistors associated with the iiat gain amplifier andthe bulge and slope networks may be located at any desired distancesaway from the control amplifiers. The thermistor included in the slopenetwork is governed in the same manner as the thermistor included in thebulge network. The thermistors may be of the type disclosed in the E. F.Dearborn application Serial No. 280,692, filed June 23,1939.

The single figure in the accompanying drawing is a diagrammatic View ofa transmission system constructed in accordance with the invention.

Referring to the drawing, a terminal or deviation gain control station Iis shown connected to a transmission line having input conductors 2 and3 and output conductors 4 and 5. The input conductors 2 and 3 areconnected by a transformer 6 to a iiat gain amplifier 1 having anegative feedback circuit 8. The negative feedback circuit 8 includesseries resistance elements 9 and I and a shunt connected resistanceelement II. The resistance element l l has negative temperaturecoeicient of resistance and is controlled by a heater coil I2. Theamplifier 1 is connected to a slope network or equalizer I3 which inturn is connected to a bulge network or equalizer I4. A resistanceelement I having a negative temperature cceliicient of resistance isincluded in the network 3 for control purposes. lThe resistance elementI5 is controlled by a heater coil I6. The bulge network I4 is providedwith a resistance element l1 having a negative temperature coefficientof resistance which is controlled A by a heater coil I8. The resistanceelements II, I5 and I1 may be of the type disclosed in application or E.F. Dearborn, Serial No. 230,692. The bulge network is connected to anampliiier I9 which in turn is connected by a transformer to the outputconductors 4 and 5.

The transmission line is not only provided with a number of carrierchannels but also with three pilot channels. The three pilot currents onthe transmission line are selected by a main filter 2I which isconnected to the transmission line beyond the amplifier i9. The filter2| which selects the three pilot currents comprises two transformers 22and 23, a crystal 24, a condenser 25 and a resistance 2S shunted acrossthe secondary winding of the transformer 23. The main lter 2l isconnected to the input circuit of an amplifier tube 21 which ispreferably of the pentode type. The amplifier 21 is provided with acontrol grid 28, an anode 29 and a cathode 30. The anode 2S is connectedto a battery 3l by a circuit including a resistance element 32 and threeauX- iliary filters 33, 34 and 35. Negative bias for the control grid 2tof the tube 21 is supplied by the potential drop across a resistanceelement 31.

rlhe three auxiliary lters 33, 34 and 35 in the output circuit of theamplifier tube 21 select the pilot currents respectively controlling theflat gain amplifier 1, the slope network i3 and the bulge network I4.The slope network I3 in the transmission line may be of the typedisclosed in the patent to H. W. Bode 2,096,027, October 19, 1937., orth'e patent to E. L. Norton, 2,019,624, November 5, 1935. The bulgenetwork I4 may be of the typedisclosed in the S. DarlingtonPatent2,l53,743, April 11, 1939. The circuit from the battery 3l to thetube 21 may be completed to ground through the resistance element 31.The alternating current circuit for the tube 21 may be completed throughthe condenser 33.

The auxiliary filter 33 which selects the pilot current governing thefiat gain amplifier 1 comprises a transformer 3S and an adjustablecondenser 40. Preferably in the circuit under consideration, this`filter selects a frequency of 12 kilocycles. The auxiliary filter 34which selects ie pilot current for controlling the slope network !3comprises a transformer 4I vand an adjustable condenser 42. The filter34 preferably in the circuit under consideration selects a frequency of56 kilocycles. The auxiliary filter 35 which selects the pilot currentfor governing the bulge network I4 comprises a transformer 43 and anadjustable condenser 44. The filter 35 in the circuit underconsideration selects a frequency of 28 kilocycles. The frequencies ofthe three pilot currents for governing the fiat gain amplifier 1, theslope network I3 and the bulge network I4 are selected lin va manner toprevent interference between the control of the Various pieces ofapparatus. Interference between the controls effected by the variouspilot currents is prevented by the construction of the networks land'the spacing of the pilot currents.

The secondary winding of the transformer 39 is connected to two oppositevertices of a bridge 45 in the vform of a voltage doubler rectifier.Voltage doubler rectifiers of this type are disclosed in the patent toD. M. Terry 2,084,115, June 15, 1937. The bridge 45 comprises twocondensers 46 and 41 and two rectiiiers 48 and 49 which are preferablyin the form of copper oxide elements. The output vertices of the bridge45` are connected across a resistance element 50 which supplies anegative bias for governing a control space discharge deviceV 5I. Thecontrol space discharge device 5I is preferably in the form of a pentodetube. The two copper oxide elements 4S and 49 in the bridge 45 areoppositely connected so as to effect rectication of each half wave of acurrent supplied thereto.

The control space discharge device 5I comprises anode 52, a contrbl grid53 and a cathode 54.V Current is not only supplied to the anode 52.power current.

` the gain desired.

from the battery 3| Vbut also alternatingV current from a low frequencysource 55. The source 55 may,'if so desired, be a local 60-cycle sourceof The circuit vfrorn'the battery 3| through the device 5| may be tracedfrom one `5 terminal of the battery 3| through a choke coil 56,secondary winding of a transformer 5l, primary windingof a transformer58, anode 52 and cathode 54 to the other terminal .of the battery 3|.The low frequency source 55 is connected to the device 5I by means ofthe transformer 51. A condenser 59 is provided for completing thealternating currentV circuit through the device 5|. The potential acrossthe resistance element 5B supplied by the voltage doubler for impressinga negative bias on the grid 53 ofthe device 5| is opposed by thepotential drop across a portion of the resistance element 6I). Thepotential drop across theresistance element 65 is provided by a battery5| which is connected to the resistance B0 :2D in series With theresistance element 62. The potential drop across the resistance element53 is opposed by the potential drop across the portion of the resistanceelement in order to ob.- tain a more than proportional change for anychange in strength of the pilot current selected Vby the auxiliaryfilter 33.

The space discharge device 5| is governed by the potential variationsacross the resistance element 50 for supplying low frequency heatingcur- (30 rent to the heater coil I2 through the transformer 58. Theheater coil I2 governs the temperature of the resistance element II tocontrol the feedback eifected by the amplifier l. If theV pilot currenton the transmission line whichconggg-5 trols the flat gain amplifier 'Iincreases in strength, the potential drops across the resistance element5I) increases to increase the negative bias on the grid 53 of Vthecontrol space discharge device V5I. This lowers the output .i430 fromthe device 5I to lower the heating current supplied to the coil I2. Thetemperature of the resistance element II is lowered togreduce the shunteiect thereof in the feedback circuit of the amplifier l. Accordingly,the feedback 0h45 the amplifier 'I' isincreased to lower the gainef.-fected by the amplifier and therefore to obtain In oase the strength ofthe pilot current on the transmission line decreases, an opposite.effect is produced to raise the gain effected by the flat gainamplifier The secondary winding of the transformer 4| in the auxiliaryfilter 34 is connected to two opposite vertices of a voltage doublerrectier 53 which is similar in construction and operation to the voltagedoubler 45 above mentioned. The auxiliary filter 34 selects the pilotcurrent employed for governing the operation of the slope network I3.The output vertices of the voltage doubler rectier 53 are connectedacross a resistance element 54 which serves to impress negative bias onthe control grid 65 of a control space discharge device 66. The controlspace discharge device 65 is similar in construction and operation tothe control space discharge device 5| and is supplied with directcurrent from the battery 3| and alternating current from the source 55.The potential drop across the resistance element S4 which is impressedon the grid 65 is opposed by the potential drop across the portion ofthe resistance element 6l. The resistance element 6l is energized by thebattery 6I. The output circuit of the control space discharge device 66is connected by a transformer 68 to the coil I6 for heating theresistance ele- 75 coil i8 b-y means of a transformer '|6.

, ment I5. The'r'esistance element I5 whichhas negative temperaturecoefficient resistance is included in the circuit of the network I3.

If the pilot current onV the transmission line which controls the slopenetwork I3 increases in strength the potential drop across theresistance element 64 is increased to reduce the output from the controlspace discharge device 66. l This reduces the low .frequency current inthe heating coil I5 to reduce the temperature of the resistance elementI5. A reduction in the temperature of the resistance .element I5increases the resistance thereof and increases the loss on the lineeffected by the slope network I3. In case the pilot current governingthe operation of. the slope network I3 is reduced in strength; belownormal value then an opposite operation to that described above takesplace. y

The auxiliary filter 35 which selects the pilot current for governingthe operation of the .bulge network I4 is connected to a voltage doublerrectifier circuit 69 by means of the secondary winding of thetransformer 43. ,The voltage doubler rectier circuit G9 is similar inconstruction and operation to the voltage doubler rectifier circuit 45.The .output vertices of the bridgegin the voltage doubler rectifier 69are connected to the terminals of the resistance element 'IIL Thepotential drop across the resistance element 'III controls the operationof a control space discharge device 'II which is similar in constructionand operation to the controll space discharge, device 5I. The device IIcomprises an anode 12, a control grid 13 and a cathode 14. The negativebias. impressed on the control grid VI3 by the drop across theresistance element I0 is opposedbyra portion of the potential dropacross the resistance element l5. The potential drop acrossthe iresistance element I5 is effected by a circuit connected to the battery6|: The anode 12 of-the device '1| is supplied with alternating currentfrom the source 55 and direct current from the battery 3| in a mannersimilar to that described with respect to the control device 5|. Lowfrequency control current from the control space discharge device II isconnected to the heating The heating coil I8 governs the temperature Voftheresistance element II for governing the operation of the bulgenetwork I4. l

If the strength of the pilot current on the transmission line whichgoverns the operation of the bulge network I4 increases in strength thepotential drop across the resistance element 1I] is increased. An`increase in the potential drop across the resistance element 'I0decreases the low frequency current output from the controlspacedischarge device II. A decrease in the output from the controlspace discharge device 'II lowers the current flow throughv the heatingcoil I8 to reduce the temperature of the resistance element I`|. Areduction in the temperature of the resistance element I`| increases theresistance thereof to increase the loss effected by the network I4.

The slope network I3 governs the slope of the attenuation characteristicof the transmission line and the bulge network I4 governs the bulge ofthe attenuation characteristic of the transmission line. The twonetworks I3 and I4 are so operated as to correct for any change in theslope or bulge of the attenuation characteristics.

Modifications in the cincuits and in the arrangement and location ofparts may be made within the spirit and scope of the invention andsuch'modications are intended'to be covered by the appendedclairns.

What is claimed is:V Y

1. In comlbination a signal transmission line 'having signal and pilotcurrents thereon, a control station, an amplifier and slope and bulgenetworks on said line at said station, and means for simultaneously andseparately controlling said amplier, said slope network and said bulgenetwork by different pilot currents .on the .transmission line to governthe iiat gain on .the line, the 'slope of the line attenuationcharacteristic andthe bulge of the line attenuation ycharacteristic.

In combinationa signal transmission line having carrier and pilotcurrents thereon, an amplier and slope and bulge networks on said line,means comprising circuits having low fre- `quency current thereon forseparately governing said amplien said slope networks and said b-ulgenetwork, and means comprising said pilot currents for separatelycontrolling said low frevquency circuits to govern the fiat gain on theline, the slope of line attenuation lcharacteristic and the bulge of theline attenuation characteristic.

3. -In combination a signal transmission line having carrier and pilotcurrents thereon, a control station, a bulge network on said line atsaid station for controlling the bulge of the line attenuationcharacteristic, a slope network on said `line at said station forcontrolling the slope of the line attenuation characteristic, Vmeanscomprising lowA frequency circuits for separately governing saidnetworks, and means for governing one of said low frequency cincuits tocontrol the ybulge of the line attenuation characteristic according tothe strength of one pilot current. on `the line and for simultaneouslygoverning another one `of said low frequencyV circuits to control theslope of the line attenuation characteristic according to the strengthof another pilot current on said line.

4. In combination a signal transmission line having carrier currents andrelatively high irequency pilot currents thereon, a contr-ol station, anamplifier on said line at said station for controlling the flat gain, a`slope network on said line at said station for controlling the slope ofthe line attenuation characteristic, a bulge network on said line atsaid station for controlling the bulge of the line attenuationcharacteristic, `and means simultaneously for controlling said amplierby one pilot current to govern the iat gain on the line, for[controlling the slope network by a second pilot current to govern theslope of the transmission line attenuation characteristic and forcontrolling the bulge network by a third pilot current to govern thebulge of the `transmission line attenuation characteristic.

5. In combination a signal transmission line having carrier currents andthree relatively high "frequency'pilot currents thereon, an amplifierand slope and bulge networks on said line, means comprising lowfrequency circuits for separately governing said amplifier to controlthe flat gain on the line, for governing said slope network to controlthe slope of the line attenuation characteristic and for governing saidbulge 'network to control the 'bulge of the line attenuationcharacteristic, and means controlled by said. pilot currents forrespectively governing the strengths of the low frequency currents onsaid low frequency circuits for controlling the amplier gain, the slopenetwork loss and the bulge network loss to maintain the energy of thedifferent frequency currents on said line the same at any desiredlevels.

6. In combination a signal transmission line having carrier and pilotcurrents thereon, a 'control station, an amplifier on said line at saidstation, a slope network on said line at said station for governing theslope of the line attenuation characteristic, a bulge network on saidline at said station for governing the bulge of the line attenuationcharacteristic, means for separating three pilot currents from thecurrents on the transmission line and for separating the three pilotcurrents, means controlled by one of said pilot [currents for governingsaid amplifier to control the flat gain on said line, means controlledby another one of said pilot currents for governing said slope networkto adjust the slope of the transmission line attenuation characteristic,and means controlled by the third one of said pilot currents forgoverning the bulge network to adjust the bulge ofthe transmission lineattenuation characteristic, said last three-mentioned means operatingsimultaneously.

F7. In combination a signal transmission line having carrier and pilotcurrents thereon, a control station, an amplier on` said line at saidstation having a feedback circuit, a first network on said line yat saidstation for governing the slope of the line attenuation characteristic,a second network on said line at said station for governing the bulge ofthe line attenuation characteristic, means for separating said pilotcurrents from the carrier currents at a point beyond said amplier andsaid networks, means for separating three of said pilot currents, meanscontrolled by one of said pilot currents for governing the feedbackcircuit of said amplifier to control the flat gain of the currents onsaid line, means controlled by a second one of said separated Ypilotcurrents for governing said rst network to adjust the slope of the lineattenuation ycharacteristic and means controlled by the third separatedpilot current for governing the second network to adjust the bulge ofthe line attenua- `tion characteristic, said last three-mentioned meansoperating simultaneously.

HENRY K. KRST.

